JP2002328295A - Focus detector and optical microscope or optical inspection apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detector which is small in the number of parts, is small in size and easy in regulation and is easy in optimization in designing. SOLUTION: This focus detector has a light source 3, a beam splitting member 15 having a surface to reflect or transmit an incident luminous flux, a beam-condensing optical system 9 for condensing the incident luminous flux, a pinhole 19 and a photodetector 21. The light source 3 is arranged in a first optical path and the beam-condensing optical system 9, the pinhole 19 and the photodetector 21 are arranged in a second optical path. The beam splitting member 15 is arranged in the position where the optical axis of the first optical path and the optical axis of the second optical path intersect. The pinhole 19 is arranged near the beam-condensing position by the beam-condensing optical system 9 and the photodetector 21 is arranged on the side opposite to the beam- condensing optical system 9 across the pinhole 19. A variable focus element 100 is arranged between the beam-condensing optical system 9 and the pinhole 19 in the second optical path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detecting device used for an optical device for observing, measuring, and inspecting an object through an optical system.

[0002]

2. Description of the Related Art In an optical device for observing, measuring, and inspecting an object through an optical system, for example, an optical microscope, an observer mounts a stage (or an objective lens) in order to clearly observe an image of the object. It is necessary to move up and down to adjust the distance between the objective lens and the object for focusing. At this time, if the magnification of the objective lens is high, the focal depth cannot be found if the stage (or the objective lens) is largely moved because the depth of focus is shallow. Therefore, the observer must move the stage (or the objective lens) little by little, and it takes time to find the focus position. On the other hand, when the magnification of the objective lens is low, since the depth of focus is deep, the observer can determine which stage (or objective lens)
In some cases, it may be difficult to determine whether the position is in focus.

In order to solve such a problem, in recent years,
These optical devices are being combined with focus detection devices. There are various types of focus detection devices. One of them is to irradiate light toward an object and detect light reflected from the object with a photodetector.
There is an active focus detection device that determines whether a focused state or an unfocused state is based on the state of reflected light.

FIG. 13 shows an example of the configuration of an active type focus detection device. In FIG. 13, 3 is a light source, 8 is a collimating lens, 15 is a polarizing beam splitter, 16 is a 波長 wavelength plate, 17 is a dichroic mirror, 11 is an objective lens,
S is a sample as an object, 9 is an imaging lens, 18 is a half mirror, 19A and 19B are pinholes, 21A and 21B.
Is a photodetector.

The light source 3 is a semiconductor laser and emits laser light in an infrared wavelength range. The polarization state is linearly polarized light. The laser beam is converted into a parallel light beam by the collimator lens 8 and enters the polarization beam splitter 15. The polarization beam splitter 15 has a characteristic of reflecting P-polarized linearly polarized light and transmitting S-polarized linearly polarized light. Therefore, if the semiconductor laser is arranged in advance so that the polarization direction of the emitted laser light coincides with the P polarization direction, all the laser light incident on the polarization beam splitter 15 is reflected by the reflection surface of the polarization beam splitter 15. Therefore, there is no loss of light intensity (light quantity).

[0006] The laser light reflected by the reflection surface of the polarizing beam splitter 15 is incident on a quarter-wave plate 16 and becomes a quarter-wave plate.
The linearly polarized P-polarized light is emitted as circularly polarized light via the wave plate 16, reflected by the dichroic mirror 17, and focused on the sample S via the objective lens 11. The laser beam reflected by the sample S passes through the objective lens 11 again, is reflected by the dichroic mirror 17, and enters the quarter-wave plate 16. The circularly polarized laser light incident on the 波長 wavelength plate 16 is
The light is emitted as linearly polarized light, but since the direction of the linearly polarized light is the S-polarized direction, all the laser light that has subsequently entered the polarizing beam splitter 15 passes through the polarizing beam splitter 15 and passes through the imaging lens 9. The light enters and is condensed via the imaging lens 9. In the optical path on the way, the light beam is split into two directions via the half mirror 18. A pinhole 19A and a photodetector 21A are arranged on the optical path of one of the split light beams at a position behind the laser beam condensing position, and on the optical path of the other split light beam, A pinhole 19B and a photodetector 21B are provided in front of the laser beam condensing position.
Is arranged. Photodiodes are used for the photodetectors 21A and 21B,
Each of A and 21B generates an electric signal corresponding to the light intensity of the laser light.

In such a focus detecting device, in the focused state, the electric signals generated by the photodetector 21A and the photodetector 21B are almost the same. In an out-of-focus state located at a position farther from the objective lens 11 than in the first embodiment, the electric signal generated by the photodetector 21B is larger than the electric signal of the photodetector 21A, and the front focus state (the sample S is higher than the focal position) Also objective lens 1
In a non-focused state at a position close to 1), the electric signal generated by the photodetector 21A is larger than the electric signal of the photodetector 21B.

As described above, since the magnitude relationship between the electric signals generated by the photodetectors 21A and 21B changes depending on the distance between the objective lens 11 and the sample S, a signal (focus error signal) obtained by taking the difference is obtained. Based on the value, it can be determined whether the object is in focus or out of focus, and further, whether the object is in the front focus state or the rear focus state. Therefore, if such a focus detection device is combined with an optical device such as an optical microscope or an optical inspection device, and the stage (or the objective lens) is moved up and down so that the focus error signal becomes zero, the sample is automatically sampled. Can be focused.

In this method, the focus detection accuracy and the focus detection capture range (up and down range of the focus detectable stage) largely depend on the diameters and positions of the pinholes 19A and 19B. By optimizing these diameters and positions, focus detection with extremely high accuracy is possible.

In this specification, a mechanism for moving a stage (or an objective lens) up and down to perform automatic focusing based on a focus error signal from a focus detection device is referred to as automatic focusing means. I will. FIG. 14 is a schematic view of an optical microscope provided with an automatic focusing unit.

[0011]

However, in the focus detection method using the above-described focus detection device, two pinholes and light are used to determine the front focus state and the rear focus state. There is a problem that a detector is required and the number of parts is large. In addition, it is necessary to secure a space for the optical path of the two photodetectors, which limits the miniaturization of the device.
Furthermore, since it is necessary to adjust each optical path individually, there has been a problem that it takes time to assemble. further,
Since the measurement accuracy greatly depends on the diameter and arrangement position of the pinhole, there is a problem that it takes time to optimize each parameter (diameter and position) at the time of design.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a focus detection device which has a small number of parts, is small, can be easily adjusted, and can be easily optimized at the time of design.

[0013]

In order to achieve the above object, a focus detecting device according to a first aspect of the present invention comprises a light source,
A light splitting member having a surface for reflecting or transmitting the incident light beam, a condensing optical system for condensing the incident light beam, a pinhole, and a photodetector, wherein the light source is disposed in a first optical path; The condensing optical system, the pinhole, and the photodetector are disposed in a second optical path, and the light splitting member is located at a position where an optical axis of the first optical path and an optical axis of the second optical path intersect. And the pinhole is disposed in the vicinity of a condensing position by the condensing optical system, and the photodetector is a focus detection device disposed on the opposite side of the pinhole from the condensing optical system. Wherein a varifocal element is disposed between the condensing optical system and the pinhole in the second optical path.

The focus detecting device according to the second aspect of the present invention includes a light source, a light splitting member having a surface for reflecting or transmitting an incident light beam, a condensing optical system for condensing the incident light beam, and a pinhole. And a light detector, wherein the light source is a first light source.
The light-collecting optical system, the pinhole, and the photodetector are disposed in a second optical path, and the light splitting member is disposed in the optical axis of the first optical path and the light in the second optical path. The pinhole is arranged at a position where the axes intersect, the pinhole is arranged near the condensing position of the condensing optical system, and the photodetector is arranged on the opposite side of the condensing optical system across the pinhole. In a focus detection device, the light-collecting optical system is a variable focus element.

Further, in the focus detection device of the first invention,
It is preferable that the variable focus element is constituted by a variable focus mirror having a reflecting surface.

Further, in the focus detection device according to the first invention or the second invention, it is preferable that the variable focus element is constituted by a variable focus lens.

Further, in the focus detecting apparatus according to the first or second aspect of the present invention, the focus change amount of the variable focus element at which the signal intensity output from the photodetector becomes constant is detected. It is preferred to configure.

An optical microscope or an optical inspection apparatus according to a third aspect of the present invention includes the focus detection apparatus according to the first or second aspect of the present invention, and automatically focuses on the basis of the amount of change in focus of the variable focus element. Is provided.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the first embodiment the present invention shown in FIG. FIG. 1 is a schematic configuration diagram of the focus detection device of the first embodiment. In FIG. 1, 3 is a light source,
8 is a collimating lens, 15 is a polarizing beam splitter,
16 is a quarter-wave plate, 17 is a dichroic mirror, 1
1 is an objective lens, S is a specimen as an object, 9 is an imaging lens, 100 is a varifocal mirror, 19 is a pinhole, 21
Is a photodetector.

The light source 3 is, for example, a semiconductor laser,
A laser beam in an infrared wavelength range (for example, 780 nm) is emitted. The polarization state is linearly polarized light. The laser beam is converted into a parallel light beam by the collimator lens 8 and enters the polarization beam splitter 15. The polarization beam splitter 15
It has the property of reflecting linearly polarized light and transmitting S-polarized light. Therefore, if the semiconductor laser is arranged in advance so that the polarization direction of the emitted laser light coincides with the P polarization direction, all the laser light incident on the polarization beam splitter 15 is reflected by the reflection surface of the polarization beam splitter 15. Therefore, there is no loss of light intensity (light quantity).

The laser light reflected on the reflection surface of the polarizing beam splitter 15 is incident on a quarter-wave plate 16 and
The linearly polarized P-polarized light is emitted as circularly polarized light via the wave plate 16, reflected by the dichroic mirror 17, and focused on the sample S via the objective lens 11. The laser beam reflected by the sample S passes through the objective lens 11 again, is reflected by the dichroic mirror 17, and enters the quarter-wave plate 16. The circularly polarized laser light incident on the 波長 wavelength plate 16 is
The light is emitted as linearly polarized light, but since the direction of the linearly polarized light is the S-polarized direction, all the laser light that has subsequently entered the polarization beam splitter 15 passes through the polarization beam splitter 15 and enters the imaging lens 9. The light enters and is condensed via the imaging lens 9.

A variable focus mirror 100 is disposed in the optical path where the light beam is being condensed, and deflects the direction of the light beam.
A pinhole 19 is arranged near the light condensing position, and a photodetector 21 is arranged behind the pinhole 19. The light detector 21 includes:
A photodiode is used to generate an electric signal according to the light intensity of the laser light.

As shown in FIG. 2, the varifocal mirror 100 includes an aluminum-coated thin film (reflection surface) 100a.
And an optical characteristic variable shape mirror (hereinafter, simply referred to as a variable focus mirror) composed of a plurality of electrodes 100b, 101 is a plurality of variable resistors respectively connected to each electrode 100b,
Reference numeral 102 denotes a power supply connected between the thin film 100a and the electrode 100b via the variable resistor 101 and the power switch 103,
Numeral 04 denotes an arithmetic unit for controlling the resistance values of the plurality of variable resistors 101. Numerals 105, 106 and 107 denote temperature sensors, humidity sensors and distance sensors connected to the arithmetic unit 104, respectively. Established 1
Optical devices.

The thin film 100a is made of, for example, P. Rai-ch
oudhury, Handbook of Michrolithography, Michroma
chining and Michrofabrication, Volume 2: Michromach
ining and Michrofabrication, P495, Fig.8.58, SPIE PR
Published by ESS and Optics Communication, Vol. 140 (1997) P187-
As in a membrane mirror described in 190, when a voltage is applied between the plurality of electrodes 100b, the thin film 100a is deformed by electrostatic force and its surface shape is changed. The shape of the electrode 100b may be selected according to how the thin film 100a is deformed, for example, as shown in FIG.

FIG. 3 is a schematic configuration diagram showing another configuration example of the variable focus mirror applicable to this embodiment. In the variable focus mirror 100 of FIG. 3, a piezoelectric element 100c is interposed between a thin film 100a and an electrode 100b, and these are provided on a support 108. And the piezoelectric element 100c
By changing the voltage applied to each electrode 100b,
By causing the piezoelectric element 100c to partially expand and contract differently,
The shape of the thin film 100a can be changed. The shape of the electrode 100b may be a concentric division as shown in FIG. 4, a rectangular division as shown in FIG. 5, or any other appropriate shape can be selected. .

In such an arrangement of the optical elements,
First, consider the case where the varifocal mirror 100 has no power. In the focused state, the laser beam passes through all the holes of the pinhole 19 and is not blocked at the outer periphery thereof.
, And the signal intensity from the photodetector 21 becomes maximum. In the rear focus state and the front focus state, the farther the sample S is from the in-focus position, the more the laser light is shifted to the pinhole 1.
9 is blocked by the outer peripheral portion of the hole 9 and the signal intensity from the photodetector 21 decreases. FIG. 6 is a graph showing the relationship between the focus position and the signal intensity from the photodetector 21 when the varifocal mirror has no power. However, in this case, the same signal strength is obtained at both the front focus position and the rear focus position. Therefore, it is necessary to determine whether the camera is in the rear focus state or the front focus state based on the signal strength from the photodetector 21 alone. Can not.

Therefore, in this embodiment, the variable focus mirror 1
By changing the focal position of 00, it is determined whether the camera is in the back focus state or the front focus state. In the front focus state, the light flux is focused on the rear side of the pinhole 19, so that the reflection surface of the varifocal mirror 100 is deformed into a concave surface, and if the curvature is optimal, the light is focused on the position of the pinhole 19. be able to. On the other hand, in the rear focus state, the light flux is focused on the front side of the pinhole 19, and if the reflecting surface of the variable focus mirror 100 is deformed into a convex surface to obtain an optimum curvature, the light flux is focused on the position of the pinhole 19. Can be done. Here, if the correlation between the amount of shift from the in-focus position on the sample surface and the amount of change in the focal position of the variable focus mirror 100 is measured in advance, the amount of defocus can be calculated. FIG. 7 is a graph showing the correlation when the focus position of the variable focus mirror is changed according to the shift of the focus position so that the signal intensity always becomes maximum. In this figure, the focal position change amount is represented as the power of the mirror. The power of the mirror is the reciprocal of the focal length obtained from the curvature R.

However, with this alone, when the operation of the focus detection device is started for the first time, it cannot be determined whether the focus state is the front focus state or the rear focus state. Therefore, the variable focus mirror 1
00 is changed so that the focal position always changes at a constant period, and the amount of defocus is calculated from the amount of change in the focal position of the variable focus mirror 100 when the signal intensity output from the photodetector 21 becomes the largest. I do.

If such a focus detection device is combined with an optical device such as an optical microscope or an optical inspection device, and the stage (or objective lens) is moved up and down so that the focus change amount becomes zero, the focus detection device is automatically turned on. The specimen can be focused.

When a 780 nm semiconductor laser is used as the light source 3, the dichroic mirror 17
A material that transmits light at 400 nm to 700 nm and reflects light at 780 nm is used. Thereby, the observation light beam transmitted through the objective lens is not affected.

As the light source 3, a red semiconductor laser which is not in the infrared region can be used. 670n
If a semiconductor laser of m is used as the light source 3, 4
A dichroic mirror having characteristics of transmitting from 00 nm to 600 nm and reflecting at 670 nm is used. Light source 3
Alternatively, a red LED or an infrared LED can be used. However, in this case, since only a part of the light rays emitted from the LED can be used, the illumination efficiency is lower than that of the semiconductor laser. Also,
It is also possible to use a half mirror instead of the polarization beam splitter 15. In that case, 1/4 wavelength plate 1
Since the number of components is unnecessary, the number of components is reduced, but the efficiency of illumination is significantly lower than that of the polarization beam splitter.

[0032] A second embodiment of the second embodiment the present invention in FIG. FIG. 8 is a schematic configuration diagram of the focus detection device of the second embodiment. In the second embodiment, a varifocal lens 200 is arranged in place of the varifocal mirror 100 (see FIG. 1) of the first embodiment, and the laser beam that has passed through the polarizing beam splitter 15 and the condenser lens 9 is transmitted to form a light beam. An optical path that does not deflect the direction is formed. In addition, the pinhole 19 is arrange | positioned near the condensing position, and the photodetector 21 is arrange | positioned behind it.

As shown in FIG. 9, the varifocal lens 200 has lens surfaces 202a and 202 as first and second surfaces.
b, a second lens 204b having lens surfaces 203a and 203b as third and fourth surfaces, and transparent electrodes 205a and 205 between these lenses.
And a polymer dispersed liquid crystal layer 206 provided through the first and second lenses 05a and 05b to converge incident light through the first and second lenses 204a and 204b. Transparent electrodes 205a, 205
b is connected to an AC power supply 208 via a switch 207 to selectively apply an AC electric field to the polymer dispersed liquid crystal layer 206. The polymer-dispersed liquid crystal layer 206 includes a large number of minute polymer cells 210 each having an arbitrary shape such as a sphere or a polyhedron containing liquid crystal molecules 209. And the sum of the volumes occupied by the polymer and the liquid crystal molecule 209, respectively.

Here, as shown in FIG.
7 is turned off, that is, in a state where no electric field is applied to the polymer dispersed liquid crystal layer 206, the liquid crystal molecules 209 are oriented in various directions. It becomes a strong lens. On the other hand, when the switch 207 is turned on and an AC electric field is applied to the polymer dispersed liquid crystal layer 206 as shown in FIG. Since the lens is oriented so as to be parallel to the lens, the lens has a low refractive index and has a low refractive power.

The voltage applied to the polymer dispersed liquid crystal layer 206 is, for example, as shown in FIG.
1 can be changed stepwise or continuously. In this way, as the applied voltage increases,
Since the liquid crystal molecules 209 are oriented such that the major axis of the ellipse is gradually parallel to the optical axis of the variable focus lens 200, the refractive power can be changed stepwise or continuously.

In the second embodiment, the varifocal lens 20
Considering the case where 0 has a certain power (it can be said that the power is zero and constant even when it has no power), as in the first embodiment, in the focused state, the laser beam passes through the pinhole 19. Since the light passes through all of the holes and is not blocked by the outer peripheral portion, all the light enters the photodetector 21 and the signal intensity from the photodetector 21 becomes maximum. In the rear focus state and the front focus state, as the sample S is further away from the in-focus position, the laser light is blocked by the outer peripheral portion of the hole of the pinhole 19, and the signal intensity from the photodetector 21 decreases. Then, in the present embodiment, by changing the focal position of the varifocal lens 200, it is determined whether the lens is in the back focus state or the front focus state.
In the front focus state, the luminous flux is focused on the rear side of the pinhole 19, so that if the varifocal lens 200 is deformed so that the positive power becomes strong and the curvature is optimized, the varifocal lens 200 is located at the position of the pinhole 19. It can be focused. On the other hand, in the rear focus state, the luminous flux is focused on the front side of the pinhole 19, so that if the varifocal lens 200 is deformed so that the positive power becomes weak and the curvature is optimized, the pinhole 19
Can be condensed. Further, the varifocal lens 200 is deformed such that the focal position constantly changes at a constant cycle, and the focus is calculated from the amount of change in the focal position of the varifocal lens 200 when the signal intensity output from the photodetector 21 becomes maximum. May be calculated.

When such a focus detection device is combined with an optical device such as an optical microscope or an optical inspection device, and the stage (or objective lens) is moved up and down so that the focus change amount becomes zero, it is automatically set. The specimen can be focused. The arrangement and operation principle of the other optical elements are the same as in the first embodiment.

[0038] shows a third embodiment of the third embodiment the present invention in FIG. 12. FIG. 12 is a schematic configuration diagram of the focus detection device of the third embodiment. In the third embodiment, the condenser lens 9 and the varifocal lens 20 of the second embodiment are used.
0 (see FIG. 8), a variable focus lens 201 having a function as an imaging lens is disposed. The variable focus lens 201 has an action of forming an image of a parallel light beam from the polarizing beam splitter 15 and By being deformed, the light can be condensed at the position of the pinhole 19. The basic operation principle of the variable focus lens 201 is the same as that of the variable focus lens 200 described with reference to FIGS.
Is the same as For other configurations and effects,
This is almost the same as the second embodiment.

As described above, the focus detection device of the present invention and the optical microscope or optical inspection device having the same also have the following features in addition to the invention described in the claims. I have.

(1) The focus detection device according to claim 1, wherein the variable focus element is a variable focus mirror having a reflecting surface.

(2) The focus detection device according to claim 1 or 2, wherein the variable focus element is a variable focus lens.

(3) The amount of change in focus of the variable focus element at which the intensity of the signal output from the photodetector becomes constant is detected.
The focus detection device according to any one of the above.

(4) An automatic focusing device comprising the focus detection device according to any one of (1) to (3), wherein the automatic focusing is performed based on an amount of change in focus of the variable focus element. An optical microscope or an optical inspection device provided with a means.

[0044]

According to the focus detection apparatus of the present invention, the number of parts is small, the size is small, the adjustment is easy, and the optimization at the time of design is easy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a focus detection device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram illustrating a configuration example of a variable focus mirror 100 used in the present embodiment.

FIG. 3 is a schematic configuration diagram illustrating another configuration example of the variable focus mirror 100 used in the present embodiment.

FIG. 4 is an explanatory diagram showing a configuration example of an electrode of a variable focus mirror 100.

FIG. 5 is an explanatory diagram showing another configuration example of the electrode of the variable focus mirror 100.

FIG. 6 is a graph showing the relationship between the focus position and the signal intensity from the photodetector 21 when the variable focus mirror has no power.

FIG. 7 is a graph showing a correlation when the focus position of the variable focus mirror is changed according to the shift of the focus position so that the signal intensity is always maximized.

FIG. 8 is a schematic configuration diagram of a focus detection device according to a second embodiment.

FIG. 9 is a diagram showing a principle configuration of a variable focus lens 200 used in the present embodiment.

10 is a diagram showing a state where an electric field is applied to the polymer dispersed liquid crystal layer shown in FIG.

FIG. 11 is a diagram showing an example of a configuration in which the voltage applied to the polymer dispersed liquid crystal layer shown in FIG. 9 is made variable.

FIG. 12 is a schematic configuration diagram of a focus detection device according to a third embodiment.

FIG. 13 is a schematic configuration diagram illustrating a configuration example of an active focus detection device.

FIG. 14 is a schematic diagram of an optical microscope provided with an automatic focusing unit.

[Explanation of symbols]

 Reference Signs List 3 light source 8 collimating lens 9 imaging lens 11 objective lens 15 polarizing beam splitter 16 quarter wavelength plate 17 dichroic mirror 18 half mirror 19, 19A, 19B pinhole 21, 21, A, 21B photodetector 100 variable focus mirror 100a thin film 100b Electrode 100c Piezoelectric element 100c-1 Substrate 100c-2 Electrostrictive material 101 Variable resistor 102 Power supply 103 Power switch 104 Computing device 105 Temperature sensor 106 Humidity sensor 107 Distance sensor 108 Support base 200, 201 Variable focus lens 205a, 205b Transparent electrode 204a , 204b Lens 202a First surface 202b Second surface 203a Third surface 203b Fourth surface 206 Polymer dispersed liquid crystal layer 207 Switch 208 AC power supply 209 Liquid crystal molecules 210 Polymer cell 211 Variable resistor S sample

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA06 DD02 FF44 GG04 GG07 GG12 GG22 LL05 LL19 LL20 LL32 2H042 DA02 DD11 DD13 DE00 DE09 2H051 AA11 AA15 CB01 CB11 GB01 2H052 AC04 AC34 AD09 AD18

Claims (3)

[Claims] 1. A light source comprising: a light source; a light splitting member having a surface for reflecting or transmitting an incident light beam; a condensing optical system for condensing the incident light beam; a pinhole; and a photodetector; Is disposed in a first optical path, and the light-collecting optical system, the pinhole, and the photodetector are disposed in a second optical path.
The light splitting member is disposed at a position where an optical axis of the first optical path and an optical axis of the second optical path intersect, and the pinhole is located near a condensing position by the condensing optical system. Wherein the photodetector is a focus detection device disposed on the opposite side of the pinhole from the condensing optical system, wherein the condensing optical system and the pin in the second optical path are A focus detection device, wherein a variable focus element is arranged between the hole and the hole. 2. A light source comprising: a light source; a light splitting member having a surface for reflecting or transmitting an incident light beam; a condensing optical system for condensing the incident light beam; a pinhole; and a photodetector; Is disposed in a first optical path, and the light collecting optical system, the pinhole, and the photodetector are disposed in a second optical path.
The light splitting member is disposed at a position where an optical axis of the first optical path and an optical axis of the second optical path intersect, and the pinhole is located near a condensing position by the condensing optical system. Wherein the photodetector is a focus detection device disposed on the opposite side of the pinhole from the condensing optical system, wherein the condensing optical system is a variable focus element. Focus detection device. 3. An optical microscope or an optical inspection device comprising the focus detection device according to claim 1 or 2, and an automatic focusing means for performing automatic focusing based on a focus change amount of the variable focus element.